DESCRIPTION OF THE PREFERRED EMBODIMENT

[0028] FIG. 1 shows a motor vehicle 10, an example of which is the heavy truck that is illustrated, having a pair of front wheels 12 for steering the vehicle, a drive axle 14 having driven wheels at opposite ends for propelling the vehicle, and an auxiliary lift axle 16 having wheels at its opposite ends. FIG. 1 shows all wheels engaged with an underlying road surface to support the weight of the vehicle. An engine within an engine compartment 18 of the vehicle propels the vehicle through a drivetrain that includes a transmission, a driveshaft and drive axle 14. Drive axle 14 comprises a differential through which its wheels are coupled to the drive shaft. The side view of FIG. 1 obviously obstructs a direct viewing of the engine, the transmission, and the driveshaft in tractor 10.

[0029] Lift axle 16 can be raised from the lowered position shown in FIG. 1 to a raised position where its wheels are lifted off the underlying surface. Raising and lowering of lift axle 16 are accomplished by a lift axle control, the pneumatic circuit portion 30 of which is shown in FIG. 2 and the electric circuit portion 32 of which is shown in FIG. 3. The lift axle control controls the operation of a mechanism that raises and lowers the lift axle.

[0030] Pneumatic circuit 30 comprises a compressed air tank 34 for holding a supply of compressed air. An inlet port of a brake relay valve 36 is connected to tank 34. One outlet port of valve 36 is connected to an air brake 38 associated with a wheel, or wheels, at one end of the lift axle, while another outlet port of valve 36 is connected to an air brake 40 associated with the wheel, or wheels, at the other end of the lift axle. Load springs 42 and 44 comprise inflatable and deflatable air springs that are disposed between lift axle 16 and the vehicle frame proximate the wheels at opposite ends of the lift axle. A formation on the exterior of each load spring provides a point of connection of a respective condui 46, 48 from valve 36 to the respective air brake 38, 40. Valve 36, conduits 46, 48, and air brakes 38, 40 are shown chiefly for reference, as they play no part in controlling the inflation and deflation of load air springs 42 and 44. When lift axle 16 is in lowered position, as in FIG. 1, load air springs 42, 44 are inflated and function as at least a portion of the lift axle suspension from the vehicle undercarriage.

[0031] An inlet port of a brake protection valve 50 is coupled to tank 34. Valve 50 has an outlet port connected through an elbow 52 and conduit 54 to an inlet port of a solenoid-operated valve 56. One port of a three-port fitting 58 is connected to one outlet port of valve 56. A second port of fitting 58 is coupled through a conduit 60 to onelift spring 62 while a third port of fitting 58 is coupled through a conduit 64 to a second lift spring 66. Lift springs 62, 66 are prime movers for the mechanism that raises and lowers the lift axle, and they are disposed proximate respective ends of lift axle 16 and in association with the lift axle suspension. The lift springs comprise inflatable and deflatable air springs that are disposed between lift axle 16 and the vehicle frame proximate the wheels at opposite ends of the lift axle. The lift axle is raised off the underlying surface by deflating load springs 42, 44 and by inflating lift springs 62, 66.

[0032] A second outlet port of valve 56 is coupled through a swivel elbow 68, a conduit 70, and an elbow 72 to an inlet port of a pressure regulator valve 74. One port of a three-port fitting 76 is connected to an outlet port of regulator valve 74. A second port of fitting 76 is coupled through a conduit 78 to load air spring 44. A third port of fitting 76 is coupled through a conduit 80 to load air spring 42. Exhaust ports adjacent the inlet port of valve 56 contain small exhaust mufflers 82, 84.

[0033] Valve 56 further comprises a solenoid 86. When solenoid 86 is energized, valve 56 assumes a condition that communicates load air springs 42, 44 with tank 34 thereby inflating the load air springs with compressed air from tank 34 while exhausting compressed air from lift air springs 62, 66 through muffler 84, thereby deflating the lift air springs. When solenoid 86 is not energized, valve 56 assumes a condition hat communicates lift air springs 62, 66 with tank 34 thereby inflating the lift air springs with compressed air from tank 34 while exhausting compressed air from load air springs 42, 44 through muffler 82, thereby deflating the load air springs. Valve 74 functions to limit pressure in the load air springs to a desired value when they are being pressurized through valve 56 from tank 34 but allows them to be exhausted when valve 56 operates to deflate them. A gauge 88 connected to valve 74 allows the load air spring pressure to be read.

[0034] Solenoid 86 has terminals 90, 92 via which it is electrically connected to electric circuit 32, shown in FIG. 3. One terminal 90 is connected to ground through an electronic system controller ESC; the other terminal 92 is connected to a terminal 94A of a two-position RAISE-LOWER switch 94. The connection may be made through a wire 96 in a wiring harness that may also contain a wire 98 for connecting terminal 90 to electronic system controller ESC, which causes ground to be applied to terminal 90 so long as the transmission is not in a reverse gear. Whenever the transmission is placed in a reverse gear, the electronic system controller ESC interrupts the ground to terminal 90, effectively creating an open circuit that prevents solenoid 86 from being energized.

[0035] In addition to terminal 94A, switch 94 comprises terminals 94B and 94C. Internally of switch 94, terminal 94A connects to terminal 94B through a normally open contact 94D, and to terminal 94C through an indicator lamp 94E. Terminal 94C is grounded, such as through a ground wire in a wiring harness connected to the switch. The drawing shows contact 94D open.

[0036] Additional circuit devices include a momentary ENABLE switch 100, and a latching relay 102.

[0037] Switch 100 comprises four terminals 100A, 100B, 100C, and 100D. Internally, switch 100 comprises an indicator lamp 100E that is connected between terminals 100C, 100D, and a normally open contact 100F between terminals 100A, 100B. Contact 100F is spring-based open, but can be momentarily closed by manual operation of an external actuator, such as a push-button for example. The drawing shows contact 100F open.

[0038] Terminal 100D is connected to ground, and terminal 100C is connected to terminal 94B. Terminal 100B is connected through a circuit protection device 104 that is fed from the vehicle ignition switch 106 when the latter is on.

[0039] Relay 102 comprises four terminals 102A, 102B, 102C, and 102D. Internally, relay 102 comprises a coil 102E that is connected between terminals 102C, 102D, and a normally open contact 102F between terminals 102A, 102B. Contact 102F is open when coil 102E is not energized and closed when coil 102E is energized. The drawing shows the coil not energized.

[0040] Terminal 102B is connected through circuit protection device 104 to ignition switch 106. Terminals 102A, 94B, and 100C are connected in common.

[0041] The condition portrayed by FIG. 3 results in solenoid 86 not being energized, placing valve 56 in a condition where load springs 42, 44 are being exhausted through muffler 82 while lift springs 62, 66 are being pressurized from tank 34, and that condition places lift axle 16 in its raised position where its wheels are off the underlying road surface. Actuation of ENABLE switch 100 followed by closing of switch 94 will energize solenoid 86, operating valve 56 to vent the lift springs and pressurize the load springs, thereby lowering the lift axle onto the underlying surface.

[0042] With ignition switch 106 having been turned on, momentary closure of contact 100F energizes relay coil 102E to close relay contact 102F. Once closed, contact 102F seals relay 102 energized because of the connection of terminal 102A to terminal 102D. Relay 102 will remain sealed until the feed from ignition switch 106 ceases, such as when the ignition switch is turned off. Lamp 100E illuminates to indicate that relay 102 is in a condition enabling the lift axle to be raised and lowered.

[0043] With relay 102 having been sealed, the lift axle will be lowered whenever switch 94 is operated closed. So long as relay 102 continues to be sealed, the lift axle may be raised and lowered by opening and closing switch 94. With relay 102 sealed and switch 94 closed, lamp 94E illuminates to indicate that the control has requested lowering of the lift axle. Otherwise the lamp does not illuminate.

[0044] When ignition switch 106 is turned off, the supply of compressed air in tank 34 enables the lift axle to be lifted off the underlying surface. Simply turning the ignition switch back on will not however result in lowering of the lift axle. Before the lift axle can be lowered, switch 100 must be actuated. If switch 94 has been left on, the actuation of switch 100 will immediately lower the lift axle; but if switch 94 had been left off, it must be turned on in order to lower the lift axle.

[0045] Anytime that the transmission is placed in a reverse gear, the electronic system controller ESC renders it impossible to lower the lift axle if it is in its raised position and will cause the lift axle, if already lowered, to immediately be raised.

[0046] While the invention has so far been described with reference to a single lift axle 16 that is on a heavy truck, the invention can be applied to vehicles having multiple lift axles. FIG. 3 shows additional solenoids 120, 122, each of which is associated with a respective additional lift axle, and each of which controls a respective pneumatic circuit like circuit 30 in FIG. 2 in the same way that solenoid 86 controls circuit 30. A respective switch 124, 126, each like switch 94, is associated with a respective solenoid 120, 122 in the same way that switch 94 is associated with solenoid 86, and the electronic system controller ESC is associated with each solenoid 120, 122 in the same way as it is with solenoid86.

[0047] The disclosed embodiment of the invention requires an intentional act on the part of the vehicle driver that is additional, and subsequent, to the act of turning the ignition switch from off to on in order to lower a raised lift axle. Yet, it retains the automatic lifting of a lowered axle whenever the vehicle transmission is placed in reverse or whenever the ignition switch is turned off. Switches 94 and 100, and switches 124 and 126 if present, are disposed where they can be conveniently accessed and viewed by the driver.

[0048] A modified form for the electric circuit portion is shown in FIG. 4. It is similar to FIG. 3, but differs in the following respects. A permanent ground connection, rather than an interruptible ground connection, is present at solenoid terminal 90. A second relay 130 is disposed between relay 102 and switch 94.

[0049] Relay 130 is a REVERSE GEAR relay and comprises four terminals 130A, 130B, 130C, and 130D. Internally, relay 130 comprises a coil 130E that is connected between terminals 130C, 130D, and a normally closed contact 130F between terminals 130A, 130B. Contact 130F is closed when coil 130E is not energized and open when coil 130E is energized. The drawing shows the coil not energized.

[0050] Relay 130 is placed in circuit between relay 102 and switch 94 with contact 130F in series between terminal 102A and terminal 94B, with terminal 130C connected to ground, and with terminal 130D connected to a source that supplies voltage for energizing the relay when the vehicle transmission is placed in a reverse drive gear.

[0051] The circuit of FIG. 4 functions with respect to raising and lowering of the lift axle in the same manner as described in connection with FIG. 3. So long as the transmission is in other than a reverse gear, the circuit of FIG. 4 is equivalent to that of FIG. 3 because contact 130F provides continuity between terminal 102A and contact 94D. However, placement of the transmission in a reverse gear will interrupt that continuity. If solenoid 86 is not being energized, interruption of that continuity is of no consequence because the lift axle is already raised. But if solenoid 86 is being energized, and the lift axle therefore lowered, interruption of that continuity will have the consequence of causing the lift axle to be raised. Relay 102 will continue to remain sealed until ignition switch 106 is turned off.

[0052] FIGS. 5 and 6 illustrate the further aspects of the invention involving fabrication of an auxiliary lift axle module 200 and its installation on a motor vehicle. Module 200 comprises a non-steerable lift axle 202 having spindles 204 at opposite ends of which wheels (not shown) are mounted. The friction brake mechanism of each air brake 38, 40 is associated with each wheel drum for braking the wheels when the service brakes are applied. Module 200 also includes brake relay valve 36, load springs 42, 44, brake protection valve 50, solenoid valve 56, 1ft springs 62, 66, regulator valve 74, and related fittings and air lines connecting them as in FIG. 2. The only pneumatic and electrical connections that are required to be made once module 200 has been installed on a vehicle are connections to the primary compressed air supply of the vehicle and to electrical wiring of the vehicle.

[0053] Module 200 further comprises its own auxiliary compressed air tank 34A that, once mounted in the vehicle, is supplied from the vehicle primary air supply. Tank 34A can however be charged with air prior to installation of module 200 on the vehicle to allow the module to be tested as a unit before it is installed in the vehicle. Hence, FIG. 2 schematically also represents module 200 with the understanding that tank 34 in that Figure corresponds to auxiliary tank 34A although. the connection to the primary vehicle supply is not specifically shown.

[0054] Module 200 comprises mounting brackets 206, 208 at opposite ends for attachment of the module to respective side rails 210 of the frame of the vehicle chassis. A respective bracket 212 atop each load spring provides for load spring attachment to the frame. A beam 214 bridges brackets 206, 208 forwardly of axle 202. Auxiliary tank 34A is fastened to the forward face of beam 214. The frame is strengthened at the location of module 200 by including an intermediate cross-member 216 between side rails 210. Each bracket 206, 208 comprises a respective flange 218 that is disposed against the outboard face of the respective side rail and that contains a set of through-holes 220, six such holes being shown. Each side rail 210 contains a matching set of through-holes 222. Opposite ends of cross-member 216 contain respective matching sets of through-holes 224. The ends of cross-member 216 fit to the inner faces of the side rails, and with the three sets of through-holes 220, 222, 224 aligned at each side rail, fasteners are used at the aligned sets to secure the parts together.

[0055] Fasteners 226 are also used to secure the ends of beam 214 to brackets 206, 208. However, holes through which fasteners pass provides for brackets 206, 208 to be positioned lengthwise of the beam (laterally in the vehicle). Prior to installation of module 200 in the vehicle, fasteners 226 are only loosely fastened to allow the brackets to be moved along the length of the beam to a limited extent. This enables the brackets to move so that flanges 218 can abut the respective frame side rails as the fasteners for securing the flanges, side rails and cross-member together are tightened. Once that has occurred, fasteners 226 are tightened. In this way, a single module can be fit securely to frames of different width.

[0056] Module 200 provides time and labor savings in vehicle assembly and reduces the complexity of the lift axle installation process. It is much easier to route air lines and mount components and devices apart from the vehicle. Installation can be accomplished without slowing a vehicle assembly line. Quality is also improved because of the ability to test the module before it is installed in a vehicle, thereby enabling defective components and/or connections to be identified earlier in the overall process.

[0057] The embodiment of FIGS. 7 and 8 is similar in many respects to that of FIGS. 5 and 6, and like reference numerals refer to the same elements in both embodiments. The embodiment of FIGS. 7 and 8 relates to a module having a steerable lift axle, as distinguished from a non-steerable one. Another difference is that auxiliary tank 34A is mounted on the rear face of beam 214.

[0058] In the two embodiments depicted by FIGS. 5-8, the valves that are communicated to the compressed air supply, as portrayed by FIG. 2, are communicated to auxiliary tank 34A. For the embodiment of FIGS. 5 and 6, the valves are disposed on the rear face of beam 214, and the beam is provided with clearance holes that allow inlet ports of the valves to be piped through the beam to the tank that is mounted on the front, or forward, face of the beam. For the embodiment of FIGS. 7 and 8 where the tank is mounted on the rear face of beam 214, the valves are disposed on the rear face of the tank and their inlet ports communicated directly to the tank. In conjunction with main tank 34, auxiliary tank 34A adds additional compressed air volume for vehicle compliance with FMVSS 121.

[0059] While a presently preferred embodiment of the invention has been illustrated and described, it should be appreciated that principles of the invention are applicable to all embodiments that fall within the scope of the following claims.